Preprints
https://doi.org/10.5194/egusphere-2025-4694
https://doi.org/10.5194/egusphere-2025-4694
08 Oct 2025
 | 08 Oct 2025
Status: this preprint is open for discussion and under review for Solid Earth (SE).

The role of fault network geometry on the complexity of seismic cycles in the Apennines

Constanza Rodriguez Piceda, Zoë K. Mildon, Billy J. Andrews, Yifan Yin, Jean-Paul Ampuero, Martijn van den Ende, Claudia Sgambato, and Percy Galvez

Abstract. Estimating the recurrence intervals and magnitudes of earthquakes for a given fault is essential for seismic hazard assessment but often challenging due to the long recurrence times of large earthquakes. Fault network geometry (i.e. spatial arrangement between faults) plays a key role in modulating stress interactions and, consequently, earthquake recurrence and magnitude. Here, we investigate these effects of fault network geometry using earthquake cycle models to generate numerous earthquakes on two different networks of normal faults in Italy: the Central Apennines, characterised by a wide network of faults offset across strike, and the Southern Apennines, a narrow fault network where faults are predominantly arranged along strike. For each region, we ran an earthquake cycle simulation on systems of seven normal faults generating approximately 150 earthquakes. In the Central Apennines, co-seismic stress transfer between faults promotes more heterogeneous stress, more partial ruptures, greater Mw variability and less periodic behaviour of large earthquakes (coefficient of variation of recurrence time, CV 0.1–0.9). In contrast, faults in the Southern Apennines experience more homogeneous stress loading, leading to a higher proportion of full-fault ruptures with more regular recurrence intervals (CV 0–0.4). In both fault networks, high long-term slip rate amplifies the effects of fault interactions: faults with higher long-term slip rate are more sensitive to positive stress perturbations from nearby faults compared to slower-moving faults. These results highlight that incorporating stress interactions from fault network geometry into seismic hazard models is particularly important for networks of faults offset across strike, where rupture behaviour is more variable.

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Constanza Rodriguez Piceda, Zoë K. Mildon, Billy J. Andrews, Yifan Yin, Jean-Paul Ampuero, Martijn van den Ende, Claudia Sgambato, and Percy Galvez

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Constanza Rodriguez Piceda, Zoë K. Mildon, Billy J. Andrews, Yifan Yin, Jean-Paul Ampuero, Martijn van den Ende, Claudia Sgambato, and Percy Galvez
Constanza Rodriguez Piceda, Zoë K. Mildon, Billy J. Andrews, Yifan Yin, Jean-Paul Ampuero, Martijn van den Ende, Claudia Sgambato, and Percy Galvez

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Short summary
We investigate how the spatial arrangement of normal faults in the Italian Apennines affects earthquake timing and size. Computer-based models show that wide networks with faults offset across-strike produce more irregular and variable earthquakes, while narrow networks with fewer across-strike faults lead to more regular events. Faster-moving faults are more sensitive to nearby positive stress interactions, highlighting the need to consider fault geometry in seismic hazard assessments.
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